Process of making polymeric acetals



Patented 151m 6, 1945 PROCESS OF 2,388,238 I MAKING POLYMERIC ACE'IALSJoseph I )ahle, West Newton, Mass.,

assignor, by

mesne assignments, to Pro-Phy-Lac-Tic Brush Company, Northampton,

of Delaware Mass, a corporation No Drawing. Application September so,1942. Serial No. 460,279

11C" a In a previous application, Serialv 0. 388,143, filed April 11,1941, I have described a new methd of treating hydroxylic basematerials, such as polyvinyl alcohol, to render them water resistant orwater insoluble, the procedure being essential ly topochemical since thebase material does not go into solution during the reaction. My presentinvention is an improvement on the invention of that application andprovides a more rapid and eflective treatment. In said previousapplication the solid hydroxylic base material, which will be referredto as polyvinyl alcohol, since that is the material on which I havebased most of the del I 4 Claims. (01. 260-73) adlhere to the sheetproducing unsatisfactory resu ts.

When insolubilizing polyvinyl alcohol; I have obtained good results witha reaction bath formed by mixing proper proportions of paraformaldehydeand isopropanol and a catalyst, such as sulfuric acid. When'the mixtureis'refiuxed a clear velopment work, is treated with a bath composed 101' a monomeric acetal, formal, and an aldehyde for instance, methyl anda catalyst. The

monomeric acetal, for instance, methyl formal,

was made and isolated and the isolated formal used in making up theinsolubilizing bath by mixing with an aldehyde and a catalyst.

My present invention is based \upon the discovery that more rapid andmore effective insolubilization is produced if the treating bath iscomposed of a mixture oi the plcyed, aldehyde, alcohol, catalyst andwater by reaction, the aldehyde-alcohol molar ratio being greater thanthe theoretical ratio required for producing the monomeric acetal. Thisbath is made by reacting the aldehyde and alcohol in the desired ratiosin the presence of a catalyst and no attempt made to separate thereaction products from the mixture. The baththus contains not only thecombined alcohol and aldehyde i. e. the monomeric acetal, the componentsof which have combined in the ratio of 1:2, but also quantities ofuncombined aldehyde and alcohol. The molar proportions of the aldehydeto the alcohol in the mixture before reaction is, preferably, within therange of 1:1 and 15:1 of aldehyde to alcohol.

The aldehyde-alcohol molar ratio is a major factor in the rate anddegree of the insolubilizing action. Thus, when the aldehyde and alcoholare present in about the exact theoretical proportions to form theacetal, namely, when the aldehyde-alcohol ratio is 1 to 2,-the degree ofthe insolubilizing action is low, while a reaction bath.

having an aldehyde alcohol ratio of upwards of 1 to 1 and 1.5 to 1producesa much more rapid monomeric acetal emsolution is obtained.solution, the water content; is due substantially to reaction betweenaldehyde and alcohol only and the concentration of aldehyde is high.Consequently, since the formal as well as the aldehyde, dissolved in theformal, are non-solvents for both polyvinyl alcohol and polyvinylformal, and the water content is negligible in this case, the reactionbath possesses naturalnon-solvent characteristics. i

In contrast to the method described in my prior application, the methodof the present invention is characterized by a rapid rate of reactionand a high concentration of aldehyde in solution. The water produced bythe acetalizing reaction is soluble in the reaction mixture and mayexert, a swelling action upon the base material. A base material may beused having a moisture content which is in equilibrium with prevailingatmospheric conditions. Consequently, drying of the base material is notessential.

- In the practice of the invention other alcohols may be used in placeof isopropanol, such as, methanol, n-propanol and butane]. The higheralcohols may be used but I prefer to employ a1- cohols containing threecarbon atoms or less because they possess good water solubility. Anyaldehydemay be used which is soluble in the mixture resulting from itsreaction with the al cohol used as long as the reaction mixture is anon-solvent for the polyvinyl alcohol or its reaction product.

The invention will be illustrated further by the followingspecific'examples.

Example 1 per 1.00 QC. sample calculated as sulfuric acid. 1

In the resulting reaction- The reacted sheeting-showed-15.8% unreacted9.1- cohol groups calculated. as vinyl alcohol.

' Example 2 Po'lyvinyl alcohol sheeting such as usedin Example 1was-treated for one minute at 70 C. in a paraform'aldehyde-isopropanolreaction mixture in which the molar aldehyde-alcohol ratio was 15 o .1,namely, in the proportion of 60 grams isopropanol'and 45 grams ofparaformaldehyde. The reacted sheeting i-showedi4.8% unreactedalcohol:groupsicaiculated as vinyl ale Example 6 i v v a Two samples ofpowdered polyvinyl alcohol 'were treated as in Example 4 except that thebaths contained also 2-mols of anhydrous sodium sulfate, Thevreactionproducts showed 39.5% v

1 and 15.8% unreacted alcohol groups calculated cohol; .The catalystcontent-of this bath was 0.9 gra s-pe'r 100 Polyvinyl alooholpowder, fscreened 'through an 1 '80 :mesh sieve {and dried in. an oven].overnightat 60 CJwa's"reactedwhiie, stirring for; seven min-' ute'sat 70 C. i'n.an isopropanolparaformaldehyde bath containing sulfuric acidasacatalys'tilgjlhe bath was prepared by reacting, until a clears'olution was obtained, 1.5 moles ofpara'iormaidehyde' (45 grams) in onemoleof isopropanol '(601gr'ams) in the presence of one per cent ofsulfuric "acid by weight on the total constit'uents'.. nthemsolubilizing reaction 60 grams polyvinyl alcohol? end 1250 grams ofbath were used.

drying, was a fine powdershowing 9.7% unreacted alcohol groupscalculated as viny alcohol. It could be molded at approximately 175C.yieltling a transparent, very tough chip Example4 i'.

Two samples or powe ed polyvinyl alcohol, dried 'at 60 C. overnight werereacted in'para formaldehyde-methanol baths for two hours at 45 0. whilestirring. The bathswere prepared by mixing paraformaldehyde 0.5 mole grain one case and 1.0 mole grams) in "the ot er cc'-.- ;calculatedfasvinyl.alcohol.

-i'1fhe reaction product, after purification and as vinyl alcohol.

My present invention is of commercial importance because the rateof'reaction is 'so high that n it is practical to practice the inventionas a continuous process in which a continuous ribbonof material. passesthrough the solubiliz'ing bath. Furthermore, the process does"away withthe necessity of reducing the moisture content below thatoffsheet storedunder. normal atmospheric con'ditions'. During ,the passage of the sheetor ribbon"through' -the bath afce'rtain amount of water is'produced-as aresult 'of; the;; reaction and the-ratio of aldehydejto; alcohol tendsto drop due to 1th'ejreaction with thepolyvinyl alcohol.

I 'iIt is possibleto-lnaintairi the bath Within desired limits: ofstrengthlby periodically or continuously 'remo vingg rtions of the bathftvhich can be 6 ireed'iromwaterby treatment with sodium sulphateor-th'e-likeand returned to the original Ibn ttli with the addition'ofandreaction with paracatalyst in which the molar proportions ofalde-.

, with 1- mole methanol 32 grams) and reacted in" the presence of oneper cent of sulfuric acid by v weight until clear solutions wereobtained,"using these solutions as insolubilizing baths.

The reaction products were white powders insoluble in boiling wateralthough -highlywater susceptible showing 68.2% and-52.2%, respectivelyof unreacted hydroxyl groups calculated as vinyl alcohol. 7 3

' Example 5 i Two samples of polyvinyl alcc hol sheeting,

0.002 in. thick, containing 15% glycerin as plasticizer were dried forone hour at 100C. and then reacted for two hours at 70" C. inparaiormaldehyde-butanol baths." These baths were prepared by reactingin one case 0.5 mole of paraformaldehyde (15 grams) with one mole ofbutanol ('74 grams) and1.5'mole of paraformaldehyde grams) with one moleof butanol (74 grams) in the other, in the presence of one per cent ofsulfuric acid by weight until the paraform had dissolved. Two phasesystems formed. In each case the top layer was used'as the infsolubilizingbath.

' forma1dehyde'.-- The {catalyst (preferably sulphurlc acid) I also isexhausted andcan' be restored as required. By theterm propanol in theappended claims, Ifinte'nd-to include-normal propanol and isopropanol. 1

1. The method of inlsolubilizingla. solid polyvinyl alcohol whichcomprises reacting amixture of an alkyl alcohol having not more.than iour carbon atoms},.an aldehyde and an acetalizatlon hyde to alcohol are;within the range of about 1:1

and, L521, said reaflctionlmixture being a solvent for the aldehyde, andtreating the solid polyvinyl alcohol in the, reactionmixture thusproduced, the polyvinylalcohol and t e final product being in the solidstate througho t the reaction.

.2. The method bi insolubilizing a solid'polyvinyl alcohol whichcomprises reacting a mixture of paraformaldehyde, propanol and anacetalization, catalyst in which the molar porportions of aldehyde andalcohol are within the range of 1 in the solid state throughout thereaction,

-The ,rea-cted sheetings were insoluble inbbilix-{gwater and showed 44.9%-and 29.5 %.-unreacted j'alcohol groups calculated as vinyl alcohol-forthe samples reacted in/the'baths having a 0.5 to 1 molaraldehyde-alcohol ratio and a 1.5 tol ratio respectively; 3 w

state throughout the reaction.

4. The method: of ins lubili'zing a solid polyvinyl alcohol which comrises reacting a mixture of isopropanol paraformaldehyde and sulfuricacid in which the molar proportions of aldehyde to alcohol arewithin therange of about 1;1 and, 15:1, and treating"the solid'polyvinylalcohol'inthe reaction mixture thus produced, the polyvinyl alcohol and the finalproduct being in the solid *Josarn DAHLE.

about 1:1 and 1.521, and treating the solid poly-'-

